VIENTIANE, LAOS — Decades after U.S. planes conducted hundreds of thousands of bombing runs over Laos, President Obama acknowledged that secret war and pledged $90 million in additional aid Tuesday to help clear unexploded bombs still strewn across the country.

“Given our history here, I believe that the United States has a moral obligation to help Laos heal,” said Obama, the first U.S. president to visit this struggling Southeast Asian nation. “And this spirit of reconciliation is what brings me here today.”

From 1964 to 1973, the United States carried out 580,000 bombing missions in Laos, dropping more than 270 million cluster bombs in a CIA-led campaign as part of the expanding regional battles from neighboring Vietnam, according to the National Regulatory Authority for UXO/Mine Action in Laos. UXO refers to unexploded ordnance.

Many of the bombings sought to cut off supplies to Vietnam, even though, officially, Laos was neutral in the Vietnam War.

Today, roughly 80 million unexploded bombs remain and continue killing and maiming dozens each year — many of them children.

In recent years, U.S. aid toward removing those bombs has slowly increased, and deaths have decreased from 300 a year to fewer than 50. Tuesday’s announcement doubled the current U.S. funding.

“We feel an urgency . . . to do our part to accelerate the clearance process,” Ben Rhodes, a deputy national security adviser, told reporters in Vientiane.

In return, leaders in Laos said they would step up efforts to recover remains and missing American service members.

Obama was just one of many leaders in the Laotian capital for the meeting of the Association of Southeast Asian Nations, whose members take turns hosting. As this year’s chair at the three-day gathering, Laos has been thrust into the spotlight — a still relatively undeveloped nation whose nominally communist government struggles with corruption, repression and economic growth.

Landlocked Laos is surrounded on all sides by more powerful neighbors that have long exploited its resources and vied for influence. In the north, China has staked its claims on land and business. In the east, Vietnam has been razing forests for years for lumber. And in the west, Thai leaders often take a paternalistic attitude to their Laotian counterparts and have been pushing for control over the Mekong River that divides them.

Laos’s economy remains fledgling and relies heavily on foreign aid. Corruption runs rampant in the government and private sector, and rights groups have complained about hard-line government policies.

Many activists have been detained or have disappeared, including renowned agricultural activist Sombath Somphone, who was dragged from his car in December 2012 in Vientiane.

Sombath has not been seen since, and Laotian officials have said only that an investigation is underway. But rights groups suspect he was taken by police.

“Pretty quickly, those talking about it and working to free him were told, ‘Shut up.’ They were told, ‘If you talk about this, you will have problems,’ ” said Phil Robertson, the deputy Asia director of Human Rights Watch.

Sombath had spent his career in rural development, teaching farmers new ways to eke out a living. And he was outspoken on inequitable land-grab deals, which have angered villagers throughout the country.

Last week at a public conference in Bangkok, Sombath’s wife, Ng Shui Meng, pleaded for Obama and other leaders visiting Laos to raise her husband’s case and the issue of human rights with Laotian leaders.

“Will the Lao leaders brush off the queries by resorting to the standard response that the police are still investigating?” she said. “I don’t know, but I hope not.”

On Tuesday, Rhodes said White House officials did raise Sombath’s case but heard back the standard response that the government is investigating and does not know where he is. The case, Rhodes said, is “something we will continue to raise” with Laotian officials. He said the topic of human rights as a U.S.-Laos issue is in its nascent phase.

“We understand and have to be mindful of the fact that we’re building a new relationship here,” he said. “We’re just beginning to have these types of conversations.”